Hybrid Cascaded Multilevel Inverter With Floating Capacitor Control
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Solution Overview
Problem
Conventional multilevel inverters face challenges in reducing system size and cost while maintaining high voltage gain, galvanic isolation, and reactive power capability, particularly in high-voltage applications, due to complex control systems and the need for multiple DC sources with specific voltage ratios.
Innovation Solution
The hybrid binary cascaded multilevel inverter (BCMLI) system employs front-end high-frequency-link converters and floating capacitors, with a floating-capacitor-voltage (FCV) control method that simplifies control and reduces the number of HFL converters, using a single DC source to generate asymmetric bus voltages and achieve high voltage gain and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multilevel inverters use multiple DC sources with specific voltage ratios to achieve high voltage gain and galvanic isolation, then the voltage gain and isolation performance are improved, but the system size, cost, and device complexity increase significantly
Solution Approach 1:
The patent combines multiple H-bridge cells with different DC voltage sources into a single cascaded multilevel inverter system. By merging the functions of multiple inverters into one unified structure, the system achieves high voltage gain and galvanic isolation while reducing overall system size and eliminating redundant components that would exist in separate inverter systems.
Solution Approach 2:
The patent segments the inverter system into multiple H-bridge cells, each connected to a different DC voltage source. This segmentation allows each cell to contribute a specific voltage level to the overall output, enabling high voltage gain through cascaded connection while maintaining modular structure that simplifies control and reduces system complexity.
2Reliability
If conventional multilevel inverters use complex control systems to maintain stable operation, then the operation stability is improved, but the control complexity and device complexity increase
Solution Approach 1:
The patent implements a control system that automatically determines switching instances based on the voltage magnitudes of the DC sources and the desired output voltage waveform. The controller self-regulates the switching of H-bridge cells to generate the appropriate step-wise voltage output, eliminating the need for complex external control mechanisms and reducing control system complexity while maintaining stable operation.
Solution Approach 2:
The control system monitors the output voltage waveform and adjusts the switching instances of H-bridge cells accordingly. By using feedback from the output voltage to determine the switching timing and sequence, the system maintains stable operation and low harmonic distortion without requiring complex predetermined control schedules.
3Adaptability or versatility
If conventional multilevel inverters use multiple DC sources to achieve wide-range power factor operations, then the power factor capability is improved, but the system size and device complexity increase
Solution Approach 1:
The patent designs the cascaded H-bridge inverter system to perform multiple functions using the same hardware structure. The same H-bridge cells and DC voltage sources that enable high voltage gain also provide the capability for wide-range power factor operations by adjusting the switching instances. This multi-functionality eliminates the need for additional components specifically dedicated to power factor control, reducing system size while maintaining versatility.
Data Source
AI summary
This disclosure provides systems, methods, and apparatus for multi-level inverters. A hybrid binary cascaded multilevel inverter (BCMLI) is discussed that includes a plurality of H-bridge cells connected in a cascaded formation. DC input voltages of some of the H-bridge cells are provided by DC voltage sources. But inputs of other H-bridge cells coupled with capacitors instead. The H-bridge cells are operated to provide an AC output voltage at the output terminals of the inverter. One or more floating capacitor voltage controllers are used to vary one or more switching instances of the H-bridge cells such that a desirable level or charge is maintained across the one or more capacitors coupled with the input terminals of the H-bridge cells.